Make sass-variables overwritable, added !default

See
http://sass-lang.com/documentation/file.SASS_REFERENCE.html#variable_def
aults_

scss/_options.scss

@@ -1,43 +1,43 @@
 // DEFAULT OPTIONS
 
 // Prefix for Hover class names
-$nameSpace: 'hvr';
+$nameSpace: 'hvr' !default;
 
 // Durations
-$fastDuration: .1s;
-$mediumDuration: .3s;
-$slowDuration: .5s;
+$fastDuration: .1s !default;
+$mediumDuration: .3s !default;
+$slowDuration: .5s !default;
 
 // Colors
-$primaryColor: #e1e1e1;
-$secondaryColor: #666;
-$highlightColor: #ccc;
-$activeColor: #2098D1;
-$shadowColor: rgba(0, 0, 0, .6);
+$primaryColor: #e1e1e1 !default;
+$secondaryColor: #666 !default;
+$highlightColor: #ccc !default;
+$activeColor: #2098D1 !default;
+$shadowColor: rgba(0, 0, 0, .6) !default;
 
 // Speech bubbles options
-$tipWidth: 10px;  //the width of the speech bubble tip
-$tipHeight: 10px; //the height of the speech bubble tip
-$tipColor: $primaryColor;
+$tipWidth: 10px !default;  //the width of the speech bubble tip
+$tipHeight: 10px !default; //the height of the speech bubble tip
+$tipColor: $primaryColor !default;
 
 // Arrows options
-$spaceBetweenTextAndArrows: 2.2em;
+$spaceBetweenTextAndArrows: 2.2em !default;
 
 // Curl dimensions
-$curlWidth: 25px;
-$curlHeight: 25px;
+$curlWidth: 25px !default;
+$curlHeight: 25px !default;
 
 // Curl colors
-$revealAreaColor: white;    // reveal area behind the curl
-$curlLineColor: #aaa;       // crease line
-$curlTransitionColor: #ccc;	// color transitioning from crease line to final color
-$curlLastColor: white;		// final color of the back of the curl
+$revealAreaColor: white !default;    // reveal area behind the curl
+$curlLineColor: #aaa !default;       // crease line
+$curlTransitionColor: #ccc !default;	// color transitioning from crease line to final color
+$curlLastColor: white !default;		// final color of the back of the curl
 
 // Browser Prefixes - Which CSS prefixes should be used?
-$webkit: true;
-$moz: false;
-$ms: false;
-$o: false;
+$webkit: true !default;
+$moz: false !default;
+$ms: false !default;
+$o: false !default;
 
 // Compile with or without classes
 $include-classes: true !default;